Lubricating oils

ABSTRACT

LUBRICANT CONTAINING AS AN ESSENTIAL INGREDIENT IMPARTING LUBRICATING PROPERTIES. ESTER OF 2,2-DIALKYLPROPANEDIOL1,3 AND MONOCARBOXYLIC ACID, WHEREIN AT LEAST ONE OF THE ALKYL) GROUPS CONTAINS MORE THAN 4 CARBON ATOMS. THE LUBRICANTS ARE WELL SUITED FOR USE IN AIRCRAFT AND GAS TURBINE ENGINES.

United States Patent 3,560,387 LUBRICATING OILS Wolfgang Schritt, Hamburg, Germany, assignor to Deutsche Erdol-Aktiengesellschaft, Hamburg, Germany, a corporation of Germany No Drawing. Filed Feb. 19, 1968, Ser. No. 706,633 Claims priority, application Germany, Feb. 23, 1967, D 52,371 Int. Cl. 'Cltlm N26 US. Cl. 252-56 5 Claims ABSTRACT OF THE DISCLOSURE 3,560,387 Patented Feb. 2, 1971 It is in the prior art to use 2,2-dialkylpropanediol-1,3 compounds as alcohol components for the manufacture of lubricating oils on the basis of esters (German Pat. 958,497, German Green Pat. 1,142,596, US. Pats. 2,798,083 and 3,148,147). The two alkyl groups in position 2 on the propanediols contain a maximum of 4 carbon atoms in these prior-art lubricating oils. The esterbase lubricating oils made from propanediols substituted in this manner are not suitable, however, for use in aircraft engines and gas turbines. The reason is that, if shortchain monocarboxylic acids are used for the esterification of these propanediols, the lubricating oils made from them have a low viscosity. This means that they have a high evaporation loss at high temperatures. On the other hand, if these propane diols are esterified with monocarboxylic acids of higher molecular weight, lubricating oils of higher viscosity are obtained, but at the same time the pour point rises so high that these oils are not suitable for the purposes in question, either. The following Table 1 shows the lubricating oil characteristics of a number of prior-art 2,2-dialkylpropanediol-l,3-diesters.

The invention relates to lubricating oils, especially for aircraft engines and gas turbines, on the basis of esters made of 2,2-dialkylpropanedi0l-1,3 and monocarboxylic acids.

Lubricating oils for aircraft engines and gas turbines must be stable and permit lubrication over a broad range oils must have a high viscosity index, so as to have a sufficiently high viscosity at operating temperature and a low viscosity at starting temperature.

It is apparent from Table 1 that the viscosity and the viscosity index definitely increase as the molecular weight increases, but that the pour point also rises.

On the basis of these facts it is to be expected that a further increase in the molecular weight of the esters will result in a further undesirable rise in the pour point.

Surprisingly, it has now been found that an increase in the number of carbon atoms in the side chains of the 2,2-alkylpropanedioll,3 compounds does not result in the expected rise in the pour point of the esters made from these alcohols, but that, contrary to this expectation, the esterification of propanediols having hexyl, octyl and decyl radicals as side chains, results in lubricating oils whose low-temperature characteristics satisfy the MIL specifications. These good characteristics are produced even when higher monocarboxylic acids are used for the 4 oils of Table 2. Furthermore the increase in the viscosity and acidity (with reference to the residual oil) is substantially slighter in the new lubricating oils, as is shown in estenfication. Table 3.

TABLE 3 [Air oxidation test at 200 0., 102 hours, 15 liters of air per hour] Percent Percent viscosity Acidity evaporaincrease, increase Ester tion loss 98.9 0. mg. KOH/g (I) Prior art:

2,2-dimethylpropanediol-l,3-dipclargonate 100 2,2-dimethylpropanediol-l,S-dicaprinate 87 380 16. 2 2,2-diethylpropanediold,3-dipelargonate 100 2,2-diethylprpanediol-1,3-dicaprinate 82 350 15. 4 hyl 2 butylpropanediold,3-dieapronate 100 Z-ethyl butylpropancdiol-l,3-dicaprylate 100 2-ethyl-c-butylpropanediol-l,3-dipelargonate 86 370 16. 2 2-ethyl-2-butylpropanediohl,3-dieaprinate. 80 320 14. 8 (II) This invention:

2-butyl-2-hexy1propanediol-1,3-dipelargonate. 51 280 9. 3 2-butyl-2-hexy1propanediol-1,3-dicaprinate- 39 270 7. 6 2-hexy1-2-octylpropanediol-l,3-dicaprylate 43 300 3. 2 2-hexyl-2-oetylpropanediol-l,3-dipelargonate 38 270 2. 6 2-hexyl-2-octylpropanediol1,3-dicaprinate. 33 250 2. 6 2-octyl-2-decylpropanediol-1,3-dicapry1ate. 32 245 2. 3 2-0ety1-2-decylpropanediol-1,3-dipe1argonate 33 240 1. 0

NOTE.PO11I points reported herein were determined in accordance with the stock point test customary in Germany. Viscosity indexes are determined from the viscosities at 100 F. and 200 F. in accordance with AS'IM, SIP N o. 168, June 1955 (American Society for Testing Materials, Special Technical Publication No. 168, Viscosity Index). The viseositics reported are in centistokes.

Accordingly, the subject of the invention is lubricating oils on the basis of diesters formed of 2,2-dialkylpropanediol-l,3 and monocarboxylic acids, which are characterized in that at least one of the two alkyl groups of the propanediol has more than 4 carbon atoms.

Esters in which the side chains of the 2,2-dialkylpropanediol-l,3 compounds contain between 6 and 14 carbon atoms are preferentially suitable as lubricating 35 bricflting Oil additive of different Composition in an Oils, according to a l f improvement of the invention. amount effective to improve the lubricating properties of The P and can be the as those used the oil, characterized in that one of the alkyl groups of in the prior art in the known esters of 2,2-d1alkylpropaneth 1 h 4 t 10 b t d th th diol'l,3. Monocarboxylic acids having 6 to 20 carbon C Propane 10 as 0 car on a Oms an e er atoms in the molecule are preferred as acid components 40 0f 531d alkyl groups has to carbon atoms, Sald dlestel of the ester lubricant oils according to the invention. being at least about 80 wt. percent of said lubricating oil. f The estef lubricating t l t g t gg; g 9 hg tg 2. Lubricating oil according to claim 1, both of said or examp e, compose a eas a on 0 y weig o the lubricating oil composition. Further, they can be alalkyl gmuPs to 10 C arbon loyed with lubricating oils on a mineral oil basis and/or 45 Lubncatmg 011 accordmg to 0131111 the acld groups mixed with 0.1 to and preferably 2 to 8%, by weight, of additives such as oxidation inhibitors, corrosion having 6 to 20 carbon atoms.

4. Lubricating oil according to claim 1, wherein the inhibitors and thickeners.

As examples of embodiments of the invention the lubricating oil characteristics of a number of esters are r listed in Table 2 below.

oil comprises a mineral oil.

5. Lubricating oil according to claim 2, the acid groups having 6 to 20 carbon atoms.

TABLE 2 Viscosity c St 980 C. 37.S C. C. Your Ester (210 F.) (100 F.) (40 F.) VJ. point 2-butyl-2-hexylpropanediol-1,3-dipclargonate 4. 08 20. 4, 662 112 60 2-butyl-2-hexylpropanediol-l,3-dieaprinate 4. 67 23. 4, 850 133 50 2-hexyl-2-oetylpropanediol-l,3-dicapronate" 3. 36 13. 01 1,890 130 Z8 2-hcxyl-2-octylpropanediol-l,3-dicaprylate. 4. 13 18. 82 2,850 138 42 2-hexyl-2-octylpropanediol-1,3dipelargonate 4. 68 23. 03 4, 060 140 70 2-hcxyl-2-oetylpropanediol-l,3 dicaprinate (of impure capric acid) 4. 89 23. 82 5, 210 144 --48 2octyl-2-decylpropanediol-l,3-dicaprylate 5. 16 25. 8 4, 880 142 68 2-oetyl-2-decylpropanediol-l,3-dipelargonate 5. 42 28. 02 5, 607 140 The esters can be produced by conventional esterifica- References Cited 2 PFOCeSSCS- d d b h UNITED STATES PATENTS n important a vantage ac leve y t e invention consists of the fact that the new ester lubricant oils have a 2499984 3/1950 et a1 25256X 2,950,250 8/1960 Fainman 25256X significantly lower evaporation loss and better stability 2 991 297 7/1961 Cool: et al 260 410 6 to oxidation than the prior-art esters of 2,2-dialkyl- 3,048,608 8/1962 Girard et al 25256X propanediol-1,3 compounds. Oxidation experiments in which 15 liters of air per hour were passed through the specimens for 192 hours at a temperature of 200 C. showed evaporation losses which were between 70 and in the case of the prior-art lubricant oils of Table l, but were only between 20 and 50% in the new lubricating 7 DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R. 

